Good information, thanks.
Your close enough to me so I'll keep my eyes open for a 203 around here.

Dennis

 

Thanks Dennis. I appreciate that.

Nelson

 

i try and save what i can. its alot harder than it used to be. thanks to the upull being in lincoln now. believe it or not there was a rust free 73-79 box there awhile ago. thanks to the forklift it got all smashed. damn ebay guy pisses me off also. takes all the easy stuff. i have a sister that live in florida maybe she can sneak one on a plane for ya when she is back up here some time. hahaha.

 

It's definitely carry-on material.

 

I did a writeup on what I have learned recently about NP203 chains and had some difficulties adding a picture along with text. I'll try again tomorrow.

Nelson

 

I have learned a few things since I posted here a few years ago and thought I would provide an update for those interested in the NP203. I have actually been meaning to post most of this info for a couple of years. I recently came across the file linked below and just made time. I have been interested in knowing how best to set up a NP203 for robustness and the chain is considered a week point by most. I personally believe the NP203 is a pretty tough unit. The attached Morse document gives horsepower ratings data for their 3/8 and 1/2 inch pitch Hy-Vo (HV) chains and other chains as well. The document does not have specific data for the HV-005 (2-1/2" wide, 3/8" pitch, 47 tooth sprockets) and HV-009 (2" wide, 1/2" pitch, 34 tooth sprockets) chains associated with the NP203 but does have generic data for HV chains with 3/8 and 1/2 inch pitch dimensions and sprocket tooth counts. I performed a data regression on the information found in the tables on page H12 and applied it to the NP203 chains and sprockets. The regression resulted in 4 polynomial equations. The 4 equations were then used to determine the HP rating at 1200 RPMs and 3000 RPMs for both the 3/8" pitch and 1/2" pitch chains and the units are in "HP per inch of width". Therefore the results have to then be multiplied by the chain width. The results multiplied by the width of each chain is as follows: The HV-005 chain (2-1/2" wide, 3/8" pitch and 47 tooth sprockets) has a HP rating of 112HP @1200RPM and 242HP @3000RPM. The HV-009 chain (2" wide, 1/2" pitch and 34 tooth sprockets) has a HP rating of 133HP @1200RPM and 295HP @3000RPM. The 2" chain has a horsepower rating increase over the 2-1/2" chain of 19% and 22% respectively at the different RPMs. From a strength standpoint, the 2" chain is the chain to use. If one wants to upgrade their 2-1/2 inch chain they will need two 34 tooth sprockets and a 2" chain. That is all that is needed. And personally I would be fine with used sprockets in good shape but I would want a new chain.

An interesting point on the strength of the chain: The Hummer H1(military version) is a full time four wheel drive vehicle and the transfer case chain (HV060) from the NP242H transfer case is 36 links with a 1/2" pitch which is the same as the NP203 2" chain. However, the width of the Hummer chain is only 1-1/4". This is a testament to the strength of the NP203.

Here are the chain part numbers I have accumulated:

2 Inch
Morse HV009
Ford D8TZ-7A029A
Dodge M880 2520-01-146-0027
Dodge 4115334
GMC 474613
New Venture Gear 13433
Cloyes 10-009C
Mile Marker 8009 or MIL8009
TRW DT9

2.5 Inch
Morse HV005
Ford D4TZ-7A029A
Dodge M880 2520-01-035-1354
Dodge 3821373
GMC 6273991
New Venture Gear 11428
Cloyes 10-005C
Mile Marker 8005 or MIL8005
TRW DT5

A couple of noteworthy points:
1) Small pitch chains are quieter than large pitch chains.
2) Larger pitch chains carry greater load.

Nelson

 

Another NP203 upgrade is a 32 spline front output shaft. As far as I can determine, this shaft was only available in some Ford trucks. I am going to go out on a limb here and say it was only installed in married NP203s behind Ford big blocks in 78 and 79. It is amazing to think of all of the big cubic inch engines from Chevrolet and Dodge that the NP203 was installed behind and that none of them had an NP203 equipped with a 32 spline front output shaft. Ford went the extra mile! This shaft would be a nice upgrade for higher HP applications. Also having 32 splines opens a whole new world for yoke options. This shaft will fit any NP203. Bearings are the same as other front output shafts but a different seal is required as the yoke is a larger diameter. National Seal 473204.

Nelson

 

On my NP203 I installed a Mile Marker model 509 Chain Saver. It is a discontinued item and they don't come up for sale very often. But one does appear every now and then. I really like the concept. It simply allows you to take the slack out of your transfer case chain. It claims to extend the life of your chain by up to 3 times. It also helps when rebuilding the transfer case as you can give yourself some slack due to the chain being a tight fit when putting things together. One nice thing about it is that the Chain Saver can be installed while the transfer case is still in the vehicle. And, you don't need to remove the chain. One interesting note is that a Ford application was an afterthought in the instructions. I have 3 copies of the instructions and the first copy I procured gave no consideration for the Ford application being a driver's drop. Following the instructions was confusing and I ended up deviating from the factory Chain Saver marks and creating my own. The second set of instructions I procured had the Ford information rubber stamped on one of the pages. The third set I ended up with had, by that time, integrated the information into the instructions. Following are some pictures of the Chain Saver.

Here is a copy of the instructions albeit a poor copy. I have a much better photocopy but the file size exceeded the limit imposed by FTE. Keep in mind that this set of instructions does not have the added information for the Ford application. I will add that when I find the copy having the added information.

Update: Here is the info added at step 10: "Note: For Ford Applications, Count 15 splines counterclockwise from the alignment mark on the rear plate assembly. This point must be used as the new alignment mark."

Btw, if the chain saver is installed on an NP203 with the 32 spline shaft, the seal included with the kit will not work. Again, Ford was an after-thought or I guess in this case a no-thought. No seal was provided in the Chain Saver kit that fits a NP203 equipped with a 32 spline front output shaft. On Motion Industries web site I was able to enter in outside seal diameter and shaft dimensions for determining what seal to use. I eventually came up with a seal part number 212518SM made by TCM. It is a thin seal but it fits.

Nelson

 

 

 

 

When I took the transfer case apart I found 2 seals on the input shaft and was confused as to why but did not give it much thought. If you look at the last 2 pictures the visible seal is in backwards. I had to turn it around. The inside seal keeps the lube inside the transfer case. The visible or outside seal keeps the lube inside the transmission and prevents it from getting into the transfer case. One could say it is effectively the transmission output seal. The seals would be face to face or back to back however one wants to look at it. And of course, for divorced configurations there is only one seal.

If I were to rebuild another NP203 I would put a sealant on the larger gaskets. I think this transfer case has a tendency to leak. It is probably in part due to bolting together several larger parts with thin narrow gaskets.

Btw, the range box in the pictures is from a divorced transfer case and I had it drilled up to mate to a Chevrolet NV4500. You can use a married range box case but you will have to plug the existing transmission mount holes before drilling the new ones for the NV4500. One gentleman on another website inferred that the mount holes for a Ford NP203 actually line up with the tail housing mount holes on a Chevrolet NV4500. I have not verified this. If true and you want a different amount of drop than factory, you will have to drill and tap more holes anyway. You will have to provide a retaining tab for the counter-gear shaft. Divorced cases come with one. This tab can be seen in the last two pictures above. It is interesting that the input shaft bearing retainer of the NP203 is a machined fit for the tail housing of the NV4500 and no modification was necessary. I believe all NP203s have the same input shaft bearing retainer. Again, if anyone knows differently please correct me. I replaced the Ford divorced input shaft with a married Chevrolet 32 spline shaft that mates nicely with the 32 spline output shaft on the NV4500. I cannot remember what the insertion depth/spline engagement was but I remember it was more than the minimum recommended. The married 32 spline Chevrolet input shaft is longer than the married Ford 31 spline input shaft. So, in a nutshell, to install a Ford NP203 behind a Chevrolet NV4500 one may have to drill up the range box with the NV4500 bolt pattern for however much transfer case drop wanted, install a Chevrolet 32 spline input shaft on the NP203, and work up a shifter mount. For any of you rock climbers out there, this is the same approach one would use to put a NP203/NP205 doubler behind a NV4500.

Nelson

 

I wanted to post a couple of pictures showing the earlier and later differential carriers (see entry #15 above). If you rebuild your NP203 it would be worthwhile to replace your carrier with the earlier unit if you happen to find you have the later one. The earlier unit is shown first below. There is actually a very early unit with eight bolts holding the carrier halves together instead of four as shown below. It is rare. The four bolt unit below I think is more than substantial. It is my understanding that the units are interchangeable as an assembly (as shown in the pictures below). I believe the internals of the later carrier can be put in either carrier as well. Nelson